Cutoff systems for severing metal tubing, roll formed shapes and extruded workpieces typically comprise a clamping and shearing assembly called a cutoff die set. The die set often comprises upper and lower shoes or platens interconnected by guide pins and bushings for reciprocal motion. Actuation is typically accomplished by means of a mechanical press having a reciprocally driven ram.
Cutoff die sets can, of course, be actuated by means of hydraulically driven presses. However, hydraulic presses are typically very large and expensive, and a mechanical press is preferred. A relatively simple mechanically driven ram press having a substantially pure vertical ram motion might comprise a ram mounted on a vertical slide and being connected to a flywheel by means of an assembly of cranks. Although this is believed to be the most straightforward approach to the design of a compact vertical ram press, several disadvantages accrue from this particular design. First, there is sliding contact between metal surfaces over the entire stroke length of the press, creating a high wear situation. The wear is aggravated by the fact that the crank arm imposes a turning moment on the ram which can result in a chattering effect wherein the ram experiences slight angular displacements and subsequent corrections in a repeating fashion over the downward travel thereof. As a result, a slide ram press may consume more of the available drive energy in moving the ram up and down than it does in driving the die set and severing the workpiece.
A substantially superior press might be achieved by eliminating the vertical slide in favor of a more efficient radial bearing assembly. A press having a ram mounted on radial bearing or pivotal links is shown in U.S. Pat. No. 3,288,011 issued Nov. 29, 1966 ot Alexander Borzym. That press comprises a long, relatively heavy ram mounted on parallelogram arms for a swinging oscillatory motion to accommodate substantial linear travel of the die set. This permits a so-called flying cut wherein the die set is accelerated up to the speed of a moving workpiece immediately prior to each cut. The substantial horizontal movement of the ram is a benefit in the flying cut in that it is in the direction of die set travel. Substantial horizontal ram movement would not be beneficial in the operation of a stationary die set.
The prior art relating to cutoff actuating presses does not teach the design of a compace lightweight press having a low inertia ram suitable for stationary die set actuation but which eliminates the disadvantages of hydraulic power and slide mounted rams.